A communication system normally comprises a network entity which provides services and the client terminals which use the services. The network entity, such as a base station, is referred to herein as a Server and the client terminals are referred herein as Clients. In the present disclosure, the terms Clients, client terminals, and client devices are used interchangeably. Also the terms Server, Network and network entity are used interchangeably.
FIG. 1 shows the data transfer that takes place between a Server and a Client after establishing communication paths between the two entities. As illustrated, the communication path from the Server to the Client is referred to herein as “downlink” and the communication path from the Client to the Server is referred to herein as “uplink.” In the downlink the Server transmits the data and the Client receives the data and this is referred to herein as “downlink data transfer.” In the uplink the Client transmits the data and the Server receives the data and this is referred to herein as “uplink data transfer.”
The data exchanged between a Server and a Client may be normally classified into two types: (i) control messages, which control the functional behavior of both the Server and the Client and facilitate the change of the attributes of the communication path; and (ii) payload data which is the user data. The control messages may be normally used to setup, maintain, and release the communication path for data transfer between the Server and the Client. A communication path between the Server and the Client is also referred to herein as a “connection.”
Normally an application is an entity that uses the connections between the Client and the Server to transfer user payload data as illustrated in FIG. 2. For example an internet browser is an application which may use any type of communication system that may establish the connections to enable this application to transfer user payload data. Examples of such communication systems include Digital Subscriber Line (DSL), Cable Modem, and Wireless Local Area Network (WLAN) which is commonly known as Wi-Fi. The 3rd Generation Partnership Project (3GPP) based wireless communication systems such as Long Term Evolution (LTE), Wideband Code Division Multiple Access (WCDMA), Global System for Mobile Communications (GSM), General Packet Radio Services (GPRS), Enhanced Data rates for GSM Evolution (EDGE), Code division Multiple Access (CDMA), etc., may also be used as communication systems.
In many applications, the uplink data transfer and the downlink data transfer are not continuous. For example in voice applications, the user's voice is digitized, buffered, processed and then transferred as a payload data. The payload data may be transferred in bursts. In some cases, the burst of data may be transferred at periodic intervals.
Often the Clients and the Server communicate over wireless media. In these wireless communication systems the Clients are often handheld battery operated devices. Hence it is important for the Clients to operate in a power efficient manner To reduce power consumption, a client terminal may turn off most of its hardware and software modules when there is no data transfer expected either in the uplink or in the downlink or both in the uplink and downlink directions.
The state in which the client terminal turns off most of its hardware and software modules is referred to herein as “sleep state.” The state in which the client terminal is involved in uplink data transfer or downlink data transfer or both is referred to herein as “active state.” To reduce power consumption in a client terminal, it may be desirable to operate the client terminal in the sleep state as much as possible while performing data transfer required by the application.
The transition from sleep state to active state of the client terminal is referred herein as “wake-up” state. The transition from active state to sleep state of the client terminal is referred herein as “entering-sleep” state. The client terminal may transition from sleep state to active state for either uplink data transfer or downlink data transfer or both. Some hardware and software modules in a client terminal may be specific to uplink or specific to downlink that can be independently turned on or turned off based on uplink or downlink data transfer requirement. Some hardware and software modules in a client terminal may be common for both uplink data transfer and downlink data transfer and may have to be turned on whenever either uplink data transfer or downlink data transfer is in progress.
The wake-up state and the entering-sleep state have the overhead in power consumption. Normally the power consumption is higher during both the wake-up state and the entering-sleep state when compared to that of the sleep state but lower when compared to that of the active state. Typically the transition time for the wake-up state is longer than the transition time for the entering-sleep state. Also in general the power consumption during the wake-up state is higher than that during the entering-sleep sate. An example of various state transitions is illustrated in FIG. 3. As and when appropriate, a client terminal may enter into sleep state and active state as illustrated in FIG. 4. For the remainder of the present disclosure, the wake-up state and the entering-sleep state may not be explicitly mentioned or shown in the drawings but they are always present.
In many communication systems, resources such as channel bandwidth may be shared by a large number of Clients to communicate with the Server. Generally different methods may be used for resource allocation. In some allocation methods the resources may be allocated at the beginning of a connection between the Client and the Server and generally not altered through the rest of the duration of the connection. In some other allocation methods the resources may be allocated at the beginning of the connection between the Client and the Server and may be altered during the duration of the connection.
Although there may be some coordination between the uplink and the downlink at the application level, in some communication systems the uplink and downlink connections may be established using separate resource allocations. In such cases there is no explicit coordination between the uplink connection and the downlink connection. The data transfer between the Server and the Client for the uplink and the downlink generally may happen at different time instances and it may not necessarily be periodic as shown in FIG. 5. For such scenarios a Client may have to separately enter into active state for the uplink data transfer and for the down link data transfer as shown in FIG. 5. This may lead to increased power consumption in the client terminals, which is a significant disadvantage for battery operated client terminals.
For some applications the uplink data transfer and the downlink data transfer may occur at periodic intervals but at different instances as shown in FIG. 6. The time interval between two consecutive uplink data transfer and between two consecutive downlink data transfer may be the same and denoted by T1. To support such applications, a client terminal may have to enter active state for the uplink data transfer and for the downlink data transfer separately as shown in FIG. 6. This may lead to increased power consumption in a client terminal, which is a significant disadvantage for a battery operated client terminals.